1. Field of the Invention
The present invention relates to position detecting devices that optically detect positions indicated by the indicating units upon an image display screen.
2. Description of the Related Art
As a device that optically detects a position indicated by an indicating unit upon an image display screen, a touch panel (touchscreen) is proposed in which, an illumination means is provided on one side of mutually opposing sides of a light-guide plate made of a translucent material and placed upon a displaying surface (screen) of a displaying device, and a light-sensor array is provided on the other side thereof; an indicating unit (input pen or stylus) that has a contacting part made of a translucent material at the unit's tip is contacted with the top surface of the light-guide plate; thereby, a position of the indicating unit is detected according to the change in the amount of light that reaches the light-sensor array (for example, refer to Japanese Patent Application Publication No. H12-172444 (2000), paragraphs 0017 through 0034, FIG. 1).